I will check with Graybeard as to whether dirtdoctor should be promoted on his website, without Sponsor Status. Bill will have the last word.
I have always tried to keep the links favored in this forum to either Educational or Govermental websites. Ones where only information and reference material is available free of charge. This has always been my ideal. Few, if any, endorsements are used here so far.
While this website does contain valuable information to the home gardener, it also promotes the sale of books and has a directory of businesses that also sell information and products.
There are Hundreds of Thousands of commercial websites that I could have used, but I have opted to keep this forum free of any sense of gardening product endorsement, unless Sponsorship is evident. There is no doubt in my mind that dirtdoctor does indeed have alot of information available free of charge, but it is not a University or a Government Agency based site.